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Causes and Solutions for Poor Welding in Multi‑Layer Aluminum Sheet Welding with Aluminum Diffusion Welders

Aug 28,2026

Aluminum diffusion welding relies on high temperature and high pressure for inter‑penetration of metal atoms to achieve solder‑free integral forming. Finished products feature low internal resistance, good toughness and high current‑carrying capacity.

Nevertheless, multi‑layer aluminum‑sheet stacking presents high process difficulty. Mass‑production often brings such defects as sound surface welds yet inner‑layer cold joints, hand‑peelable delamination, local incomplete fusion, stress‑induced cracking and over‑heating under current.

I Process Difficulties of Multi‑Layer Aluminum‑Sheet Diffusion Welding

1.Multi‑layer stacking creates numerous gaps; internal air is hard to expel and easily trapped between layers to form voids that block metal bonding.

2.Aluminum oxidizes readily. Oxide films form on every sheet surface; their blocking effect multiplies after stacking and hinders atomic inter‑diffusion and fusion.

3.Aluminum conducts heat fast. Outer layers heat‑up rapidly while inner layers heat‑up slowly, producing pseudo‑welds where outer layers are well‑welded but inner layers remain unfused.

4.Multi‑layer sheets tend to receive uneven pressure. Slight mold irregularity may cause compaction in central zones and suspended cold joints at edges.

II Core Causes of Poor Welding for Multi‑Layer Aluminum Sheets

1.Inadequate sheet‑surface cleaning; oxide films and impurities block fusion

During storage and cutting, aluminum‑sheet surfaces quickly generate hard oxide films that cannot participate in welding fusion. Residual oil stains, dust and hand sweat turn into isolating impurities under high temperature. After multi‑layer stacking, barriers exist between every layer; only superficial contact is obtained instead of real metallurgical bonding, leading to delamination upon later‑stage force and vibration.

2.Irregular stacking; air trapping and excessive inter‑layer gaps

Cut aluminum sheets tend to warp, vary in tightness and bulge with offset. Direct feeding for welding quickly compresses and seals superficial gaps and locks internal air to form numerous hidden voids. Appearance looks smooth, yet inner bonding remains loose and delamination occurs under force or vibration.

3.Improper matching of welding pressure

Insufficient pressure fails to compress inter‑layer gaps and break oxide films; inter‑layer contact stays loose and fusion is incomplete. Excessive pressure collapses and hardens outer aluminum sheets instead, locking middle‑layer gaps and producing inner‑layer cold joints, accompanied by sheet thinning, deformation and brittle cracking. Multi‑layer welding shall avoid brutal high‑pressure squeezing and adopt staged stabilizing‑pressure slow compaction.

4.Insufficient temperature and holding time; inadequate inner‑layer heat penetration

Multi‑layer aluminum sheets store large heat and conduct heat slowly. Temperature and duration for single‑layer welding only realize outer‑layer fusion; heat cannot fully penetrate middle and inner layers. Outer‑layer atoms complete diffusion forming while inner‑layer temperature does not meet requirements, resulting in pseudo‑welds. Meanwhile excessive temperature and overlong holding time soften aluminum sheets and embrittle crystal grains and lower overall strength.

5.Uneven pressure and heat due to irregular molds

Worn, carbon‑deposited, bumpy graphite molds or pressure plates with poor parallelism cause uneven pressure‑heat distribution over multi‑layer sheets. Frequently‑seen phenomena: sound central welding with edge delamination, or one‑side cold joints.

6.Wrong heating‑cooling sequence generating welding stress

Too‑fast temperature rise closes superficial gaps in advance and traps internal air and impurities. Immediate pressure release and part removal after welding produce inconsistent shrinkage speed for multi‑layer sheets, tearing incompletely‑formed bonding layers and generating micro‑cracks, leading to post‑cooling delamination and decreased tensile strength.

7.Mixed incoming‑material batches with inconsistent sheet conditions

Mixed production of new‑and‑old aluminum sheets, sheets of different oxidation degrees, thickness and hardness brings varied contact and stress states for each layer, disordered pressure transmission, compaction in some layers and suspension in others, and highly unstable batch‑wise quality.